"To bend a small bubble of space in a similar fashion for transport purposes, we'd need to solve relativity's equations to create a density of energy that's lower than the emptiness of space. While this kind of negative energy happens on a quantum scale, piling up enough in the form of 'negative mass' is still a realm for exotic physics."
https://www.sciencealert.com/faster-than-light-travel-is-possible-within-einstein-s-physics-astrophysicist-shows
"density, mass of a unit volume of a material substance. The formula for density is d = M/V, where d is density, M is mass, and V is volume. Density is commonly expressed in units of grams per cubic centimetre. For example, the density of water is 1 gram per cubic centimetre, and Earth’s density is 5.51 grams per cubic centimetre"
https://www.britannica.com/science/density
Mass
"the local interstellar medium contains approximately 40% more hydrogen atoms than some prior studies suggested."
"the number they found was 0.127 particles per cubic centimeter, or about 120 hydrogen atoms in a space the size of a quart of milk."
https://www.nasa.gov/solar-system/new-evidence-our-neighborhood-in-space-is-stuffed-with-hydrogen/
Volume
"The size of the solar system is defined by the volume of space over which the sun’s influence exceeds those of other nearby stars in the Milky Way galaxy. This influence derives from two fundamental forces of nature: gravity and magnetism."
https://www.space.com/the-universe/solar-system/how-astronomers-work-out-the-size-of-the-solar-system
Density
"Beyond gases, there’s another state of matter called plasma. And it makes up 99.9% of the observable universe."
https://www.nasa.gov/podcasts/curious-universe/plasma-plasma-everywhere/
